1. Field of the Invention
The present invention relates generally to electrical switching apparatus and, more particularly, to an interlock assembly for safety switches. The invention also relates to safety switches employing an interlock assembly.
2. Background Information
Safety switches are used in electric power distribution systems in order to isolate a load or a portion of a power circuit.
General duty safety switches are used, for example, in applications where electrical current ranges from about 30 amperes through about 100 amperes.
For instance, general duty safety switches are commonly employed in residential and commercial applications and are suitable, for example, without limitation, for light duty motor circuits and service entrance applications.
FIGS. 1 and 2 show a representative general duty safety switch 2. As shown, the safety switch 2 generally includes a switch mechanism 4 housed within an enclosure, such as sheet metal cabinet 6, having a cover 8 (not shown in FIG. 2). The switch mechanism 4 has a number of switch blades 10,12,14 (three switch blades 10,12,14 are shown for 3-pole safety switch 2 of FIG. 2) mounted along a rotatable switch shaft 16. The shaft 16 is rotated by an operating handle 18 pivotally coupled on the outside surface of one side wall 20 of the enclosure 6 and coupled to the shaft 16 by a spring-toggle mechanism 22 on the inside surface of the side wall 20. The spring-toggle mechanism 22 provides a snap action to ensure that the safety switch 2 opens and closes rapidly when the handle 18 is actuated. A more detailed explanation of the components of a safety switch and operation thereof, is provided in U.S. Pat. No. 6,373,009 (disclosing a fail safe arrangement which assures positive operation of the switch spring-toggle mechanism).
As discussed in U.S. Pat. No. 6,373,009, each switch blade 10,12,14 has a first end and a second end. When the safety switch 2 is closed or in the ON position as shown in FIG. 2, the first ends each engage a corresponding line contact 24,26,28 while the second ends respectively engage corresponding load contacts 30,32,34. Line terminals 36,38,40 provide electrical connections between line conductors (not shown) and the respective line contacts 24,26,28. The load contacts 30,32,34 are electrically connected to a first set of fuse clips 42,44,46, respectively. Fuses 48 (only one fuse 48 is shown in FIG. 2) interconnect each of the first fuse clips 42,44,46 and the corresponding second fuse clips 50,52,54, which, in turn, are electrically connected to load terminals 56,58,60, respectively. The fuses 48 provide overcurrent protection.
The switch mechanism 4 is operated between the OFF (not shown) and ON (FIG. 2) positions by an operating assembly 62, best shown in FIG. 3. The operating assembly 62 includes a bracket 64 which is secured to the side wall 20 of the cabinet 6 by fasteners, such as screws 66. The screws 66 are received in indented portions 68,70 which space or offset the bracket 64 from the inner surface of the side wall 20. The bracket 64 includes an aperture 72 defining a pivot axis. The operating assembly 62 further includes the aforementioned spring-toggle mechanism 22 which has a U-shaped operating member 74 with first and second legs 76,78 extending from a base 80. The U-shaped operating member 74 pivots about the pivot axis in response to movement of the operating handle 18. Specifically, the base 80 of the U-shaped operating member 74 is coupled to an arm 82 on a drive link 84 by a spring 86 and is, therefore, spring-biased. The first leg 76 of the operating member 74 is pivotally disposed within the space defined between the offset bracket 64 and the inside surface of the cabinet side wall 20. The operating member 74, drive link 84 and operating handle 18 pivot about the pivot axis via a pivot pin 88 inserted through aperture 72. The operating handle 18 is partially covered by a shroud 90 within which it can pivot between the ON (FIG. 2) and OFF (not shown) positions. Accordingly, when the operating handle 18 is pivoted, the drive link 84 coupled thereto pivots causing the U-shaped operating member 74 to pivot and actuate the aforementioned switch mechanism 4.
The spring 86 between the U-shaped operating member 74 and the drive link 84 provides the aforementioned spring-bias to the operating assembly 62 in order to enable the nearly instantaneous response or snap-like reaction when the operating handle 18 is moved. Thus, the safety switch 2 can be actuated very quickly when necessary, for example, in order to overt a dangerous electrical condition. While the foregoing operating assembly, the spring-toggle mechanism therefor, and the snap action it affords represent significant achievements in the art, known safety switches continue to suffer from a unique set of disadvantages, one of which poses a potential safety threat.
Specifically, the design of most known 30–100 Ampere General Duty safety switches, for example, allows the switch mechanism to be operated when the enclosure cover or door is open. This presents a potential safety issue, wherein an operator could be exposed to the arcing or sparking typically produced when energizing or opening a circuit.
There is a need, therefore, for an improved safety switch which resists operation of the handle when the switch enclosure is open.
There is, therefore, room for improvement in safety switches.